D-Day is made up of the first 6 Theaters of War:
1.1 Into the Fray
1.4 Second Wave
1.5 Call of Duty
The description above all the Theaters of Wars in the list is "June 6, 1944--D-Day. Today we partake in an all out offensive to crush the enemy. Jerry's dug in deep, but we can't stop until the beach is ours! Next stop: Omaha Beach!"